Ubuntu & Wordpress: setting wildcard domain?

Hi,

I'm a Linux noob ...

So I've managed to install Wordpress on my new Ubuntu server but now I want to activate the WP Network option. In order to do this I need to set a domain wildcard for my Ubuntu server

This page (http://codex.wordpress.org/Migrating_Multiple_Blogs_into_WordPress_3.0_Multisite) tells me to do this:

Create a wildcard subdomain. This should be as easy as going into cPanel and creating a subdomain named *.

But I don't have cPanel ... I'm working on a local server.

So how would I do this (I'm connected to my Ubuntu server via PuTTY)? Step by step please, as I don't know much about the Linux CLI ...

Thank you very much!

Jerome